The present invention relates to an X-ray CT (computed tomography) data acquisition method and an X-ray CT apparatus, more specifically to an X-ray CT data acquisition method and an X-ray CT apparatus which allows projection data to be acquired for reconstructing a CT image at a slice position outside the linear displacement range in for example the helical scan, the helical shuttle, and the variable helical pitch scan.
There is already known an X-ray CT imaging method for reconstructing an image at a slice position outside the linear displacement range in the helical scan, i.e., relative displacement range in the direction of helical axis with respect to the imaging object of the X-ray tube (for example, see patent JP-A-2005-137389).
To reconstruct a CT image, the projection data of the view angle range over 360 degrees in the full reconstruction mode is required, and the projection data of the view angle range over 240 degrees, for example, in the half reconstruction mode is required.
However, in the Prior Art described above, the rotating movement and the linear movement are started and terminated at the same time at the starting point and at the end point of the linear movement. There arose a problem that, if either the rotating velocity is too slow or the linear movement velocity is too fast, acquirable position may be passed over before acquiring the projection data of the view angle range required to reconstruct the CT image at the slice position outside the linear movement range.
The object of the present invention therefore is to provide an X-ray CT data acquisition method and an X-ray CT apparatus which positively acquire the projection data for reconstructing the CT image at the slice position outside the linear movement range in such scan method as the helical scan, the helical shuttle, and the variable helical pitch scan.